Sound record



March 14, 1939. G. L. lDlMMICK SOUND RECORD Original Filed Jun 4, 1931 I N V E /V 7'08 .llommwhj SIGNFIL HMPLIFIER RECTIFIER FIND HMPLIFIER GLerm/L Patented Mar. 14, 1939 UNITED STATES SOUND RECORD Glenn L. Dimmick, Haddonfield, N. J., assignor, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Original application June 4, 1931, Serial No.

541,976. Divided and this application December 29, 1934, Serial No. 759,652

13 Claims.

My present invention relates to sound records, and more particularly to a sound record of the type disclosed in my copending application Serial No. 541,976, filed June 4, 1931, now Patent No. 1,999,721, granted April 30, 1935, of which the present application is a division.

In reproducing sound from a film of this type,

the film is passed from a feed drum or reel, past a fine line of light extending in a direction transverse to the direction of travel of the film, and thence to a take-up reel onto which the film is wound. Heretofore, it has been common practice, according to one well known method, to record the sound on the film in the form of a single sound trace or line, part of which is substantially uniformly transparent and part of which is substantially uniformly opaque, each part varying in area in accordance with the recorded sound. To obtain faithful reproduction of the sound from a record of this kind, it is essential that the reproducing light beam extend over the full width of the sound track on the film. It happens occasionally, however, that the reproducing light beam does not completely cover the sound track as, for example, due to a slight movement of the film transversely of the direction in which it is fed as above described, or due to accumulation of dirt or other foreign matter in the reproducing slit, and in such cases, there results distortion of the reproduced sound.

Another disadvantage of a single trace record produced according to the variable area method above described resides in the fact that the peaks of the high frequencywaves usually are somewhat under-exposed at large amplitudes. This results in cutting off a portion of the high frequency response during reproduction and constitutes another source of imperfect reproduction. Obviously, therefore, it is desirable, in this method of recording, that the density of the film be independent of the amplitude of the .recorded wave and as uniform as possible.

In accordance with my invention, I record the sound within the space or track allotted to 2; record of a single sound line, but instead of recording the sound. in the form of a single sound line, I record it in the form of a plurality of substantially identical sound .lines, each being a true representation of the wave form of the recorded sound but having an amplitude smaller than a record of a single sound line. Thus, should the reproducing light beam fail to completely cover the sound track for any reason, or should the light beam reaching the film not be uniform,little or. no appreciable distortion results when using a record according to my invention, since each section of my multiple sound line record is an independent record of the recorded sound. Fur thermore, since the sound is recorded in a plurality of lines within the space normally con- 'taining a single sound line, as was the practice heretofore, the ratio of the amplitude of each of my plurality of sound lines to the amplitude of the single sound line will be inverse to the ratio of the number of sound lines recorded to the single sound line or unity, the sum of the amplitudes of the plurality of sound lines being equal to the amplitude of the single sound line representing the same recorded sounds. Consequently, the peaks of the high frequency waves of each individual sound line will be much smaller and the exposure much more uniform than in the case of a single sound line record, the distortion resulting from under-exposure of these peaks being greatly diminished, I am thus able to attain the primary object, of my invention, namely, to produce a. photographic sound record of the variable area type which will not be subject to the disadvantages present in the single sound line records of the type previously employed.

Another object of my invention is to providea photographic sound record which will not be dependent upon the accurate dimensions of the reproducing light beam for the faithful reproduction of sound therefrom.

Still another object of my invention is to provide a photographic sound record in which the peaks of the high frequency waves will be sufficiently exposed to result in proper reproduction of sound therefrom.

The novel features of my invention are set forth with particularity in the appended claims, the invention itself, however, both as to its organization and method of operation, together with additional objects and advantages thereof, being best understood from the following description of a specific embodiment, when taken in connection with the accompanying drawing in which Figure 1 is a diagrammatic view, in perspective, of a sound recording system for forming a record according to my invention, and

Fig. 2 is a fragmentary detail view of my improved sound record.

Referring to the drawing, wherein similar reference characters indicate corresponding parts throughout, there is shown, in Fig. 1, a sound recording system which forms the subject matter of and which is claimed in my above-identified copending application. This system comprises a recording light source in the form of an incandescent lamp I which is focused, by means of a suitable lens 2, upon a galvanometer mirror 3, mounted for rotation about an axis 44. An opaque light stop 5, having an opening therein into which project the saw-tooth projections 6, for. defining a plurality of saw-tooth light beams, is disposed adjacent the lens 2 in the manner shown and is focused, by means of a lens I, upon a narrow slit 8, formed in an opaque plate or disc 9 and having its axis parallel to the mirror axis 44. The galvanometer mirror 3 is focused by means of a lens Ill upon an objective lens H,

which in turn focuses the slit 8 upon the sound track T of a negative film F which may have a series of pictures or scenes S recorded thereon, as in the usual so-called talking movie fihns. In such films, the sound track T may be of standard width and comprises the space allotted to the single sound line record commonly found thereon.

Normally, the light stop 5 is so located that, when there is zero modulation, or when the mirror 3 is stationary, the image 6a of the sawteeth 6 overlaps the slit 8 in such a position that the slit intersects the altitudes of the small triangular saw-teeth images substantially midway thereof, leaving only the spaces 8a, 8b, 80, and 811 through which the light may pass, since both the stop 5 and the plate 9 are opaque. The light beam I2 is thus divided into a plurality of beams l2a, i217, I20, and lZd which are focused, as above described, onto the sound track T by the objective lens H, each of the divided beams 12a, l2b, 82c, and I2d individually and independently affecting a portion of the light sensitive track T. As the mirror 3 vibrates about its axis 4@ in response to sound impulses impressed upon a suitable microphone in circuit therewith (not shown), the image 6a moves up and down across the slit 8, thereby correspondingly shortening or lengthening the spaces 8a, 8b,.8c and 8d to vary the width of each of the recording beams I2a, I22), I20 and l2d. In this manner, as the film F is advanced, a plurality of similar areas on the track T are simultaneously exposed to the effects of the variable rec'ording light beams l2a, I21), I20 and 1211, each area resulting in an individual sound line on the track T.

In the drawing, I have shown the saw-tooth stop 5 as cooperating with the light slit 8 to divide the recording light beam I2 into four paths or beams l2a, [2b, l2c, and l2d. Obviously, the beam I2 may be divided into any number of individual beams desired by merely changing the number of saw-teeth shown at 6. As shown in r the drawing, the four separate and divided light beams will affect four separate paths on the track T to produce four separate and identical sound lines thereon. When a positive P is printed from a negative F so produced, the resulting record will appear as in Fig. 2. The clear areas 22a, 22b, 22c, and 22d correspond, respectively, to the Portions on the negative afiected by the light beams 12a, I21), I20, and l2d, while the opaque or dark portions 25, 26, 21, 28 and 29 correspond to the unaffected portions of the negative track T.

It is well known that during reproduction from a record of the variable area type, the accumulation of foreign matter such as dirt, oil, scratches, etc. on the transparent area of the record results in the production of ground noises. Thus, it is essential that the amount of clear or transparent area be reduced to a minimum if the ground noise is to bereduced. To this end, various proposals have been made, among them being one'by which some of the audio frequency current is rectified as by a rectifier 3t and the rectified current passed through the galvanometer winding 3! in such, a direction that the recording light beam vibrates about a new mean position on the sound track which is a function of the amplitude of the sound being recorded, where-a single sound line is being recorded thereon (see article entitled Ground noise reduction" appearing on pages 12 to 14. of

the Motion'Picture Projectionist for March, 1931, volume 4, #5). The chief disadvantage of this method is that when the modulation is small, the recording is close to the edge of the track, and, in the case of imperfectly adjusted reproducers employing a single sound line record made by this process, it sometimes happens that the scanning beam does not cover the full width of the sound track, as heretofore described. This usually results in distortion due to cutting off of the small amplitude recordings. I

According to my invention, I can easily overcome this difficulty by merely placing the stop 5 originally in such a position that, instead of the image 6a of the saw-teeth 6 falling on the slit 8 as above described when there is no modulation, the image 6a will so be caused to fall on the slit 8 that the slit will traverse the image 6a close to the bases of the small triangles. As the amplitude of the recorded signals changes, the rectified A. C. may be caused to shift the position of the image 6a toward or away from the position shown in Fig. 1, as the case may be. By positioning the stop 5 in this manner, the beams l2a, I2b, Ho, and i211 are, for small amplitudes, relatively narrower than when the stop 5 is positioned as first described above. Hence, when the positive P is printed, the transparent areas 22a, 22b, 22c, and 22d will be relatively narrower and the opaque areas 25, 26, 21, 28, and 29 will be relatively wider. Due to the decreased clear area on the film resulting thereby, ground noise is materially reduced during reproduction, and at the same time, the distortion, if any, resulting from the fact that the scanning beam does not fully cover the sound track, is greatly reduced because each sound line is a complete, individual, and independent record of the recorded sound, and only one or a portion of one of said individual records may be affected by the improperly positioned scanning beam.

A further advantage resulting from the employment of the recording system such as here described in the saving of power employed to drive the galvanometer mirror. It is well known that the power required for this purpose goes up as the square of the amplitude of the sound recorded.

Obviously, where four double sound lines, for example, are formed on the same negative track on which a single sound line of the same sounds is normally recorded, the mirror need be vibrated through only one-eighth the are normally necessary. Thus, only one sixty-fourth of the power is required to record the same sounds, and since the amplitudes of all of the sound lines are added during reproduction, the total amplitude resulting will be the same as that of a single line record of the same sounds on a track of the same width as that on which all four double sound lines have been recorded.

It will further be apparent that the sound lines of my invention have amuch more uniform exposure at high frequencies than the high frequency waves of the single sound line of a variable area record on the same track resulting in the same output. The exposure of a sound line is dependent upon the cross velocity of the recording beam, which is, of course, at right angles to the direction in which the film F is fed. The maximum cross velocity of the recording light beam is directly proportional to the frequency for a constantamplitude. For a constant frequency, the maximum cross velocity is proportional to the amplitude. It-is the efiect of the cross velocity, as hereinbefore stated, which is'responsible for the under-exposure of the peaks of the high frequency waves and for the cutting 01! a portion of the high frequency response during reproduction. By using a record in which the sound has been recorded in a plurality of sound lines, the effect of cross velocity is reduced in direct proportion to the number of lines in a given sound track width.

From the foregoing description, it will be apparent that a sound record formed in accordance with my invention is particularly useful for wide films such as have come, more or less, into use recently, since 'such films are particularly diflicult to feed through the reproducing apparatus without slight movement to one side or the other. However, it is to be distinctly understood that my invention is not necessarily limited to this type of film. Furthermore, although I have shown and described my invention in connection with a sound recording system, it will be apparent to those skilled in the art that the invention may be advantageously employed in re-recording systems as well as recording systems. I am also fully aware that, although I have shown a certain specific embodiment of my invention, many modifications thereof are possible. The invention is, therefore, not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. In a combined sound and picture film, a sound record within the space normally allotted for a single sound track, said record comprising a plurality of substantially identical sound tracks each delineating a wave front of the same sound and the sum of the transparent areas of the tracks in said space having a mean width which decreases as the amplitude of the sound decreases. 4

2. In a combined sound and picture film, a sound record within the space normally allotted for a single sound track, said record comprising a plurality of substantially identical'sound tracks each delineating a wave front of the same sound, said tracks having their corresponding portions aligned transversely of the film and the transparentareas of said tracks having mean widths which decrease as the intensity of'the sounds to be recorded decreases.

3. A sound record comprising a plurality of separate opaque sound tracks on a transparent base, each of said sound tracks delineating a wave front of the same sound, and the total transparent area of said record being a minimum consistent with the ability of said record to modulate a reproducing light beam for reproduction of sounds of low amplitude and a total maximum transparent area beingconsistent with the total width available for said sound tracks for reproduction of sounds of large amplitude, the mean variation between said minimum and maximum areas being a function of the amplitude of the sound to be reproduced.

4. A photographic sound record comprising a plurality of separate transparent sound tracks on an opaque base, each of said sound tracks delineating a wave front of the same sound, said sound tracks being adjacent each other with their corresponding portions transversely aligned and the total transparent area of said record being a minimum consistent with the ability of said record to modulate a reproducing light beam for reproduction of weak sounds and a maximum consistent with the ability of said record for reproduction of strong sounds, and having a mean variation between said minimum and maximum varying as a function of the intensity of the sound to be reproduced.

5. A negative photographic sound record comprising a plurality of separate opaque sound tracks on a transparent base, each of said sound tracks delineating a wave front of the same. sound, said sound lines being adjacent each other with their corresponding portions transversely aligned and the ratio of total opaque area to total transparent area of said record being a maximum consistent with the ability of said record to record sounds of large amplitude and the ratio of the-total opaque area to total transparent area being a. minimum consistent with the ability of said record to record sounds of small amplitude, the mean variation between said ratios varying as a function of the amplitude of the sound to be recorded.

6. A photographic sound record of the varying width constant density type having two separate traces representing the'same sounds and located on the two sides of a longitudinal axis, and in which the positive record hrsv a transparent sound track along its axis which is bounded by said two traces, the transparent sound track having a mean width which decreases as the amplitude of the sound decreases.

7. A sound record according to claim 6 and in which the troughs of the traces are located substantially parallel to the edges of the film near the axis of the sound track.

8. A photographic sound record of the varying width constant density type having two separate traces representing the same sounds and located on the two sides of a longitudinal axis, and in which the record has a transparent sound track along its axis which is bounded by said two traces, the transparent sound track having a mean width which decreases as the amplitude. of the sound decreases.

9. A sound record according to claim 8 and in which the troughs of the traces are located substantially parallel to the edges of the film near the axis of said sound track.

10. A photographic sound record of the varying width constant density type having two separate traces representing the same sounds andlocated on the two sides of a longitudinal axis,

and in which the negative record has an opaque sound track along its axis which is bounded by said two traces, the opaque sound track having a mean width which decreases as the amplitude of the sound decreases.

11. A sound record according to claim 10 and in which the troughs of the traces are located substantially parallel to the edges of the fllm near the axis of said opaque sound track.

12. A photographic sound record of the varying width constant density type having two sepa- 

